Direct composite resin fillings versus amalgam fillings for permanent or adult posterior teeth

  • Review
  • Intervention

Authors


Abstract

Background

Amalgam has been the traditional material for filling cavities in posterior teeth for the last 150 years and, due to its effectiveness and cost, amalgam is still the restorative material of choice in certain parts of the world. In recent times, however, there have been concerns over the use of amalgam restorations (fillings), relating to the mercury release in the body and the environmental impact following its disposal. Resin composites have become an esthetic alternative to amalgam restorations and there has been a remarkable improvement of its mechanical properties to restore posterior teeth.

There is need to review new evidence comparing the effectiveness of both restorations.

Objectives

To examine the effects of direct composite resin fillings versus amalgam fillings for permanent posterior teeth, primarily on restoration failure.

Search methods

We searched the Cochrane Oral Health Group's Trials Register (to 22 October 2013), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 9), MEDLINE via OVID (1946 to 22 October 2013), EMBASE via OVID (1980 to 22 October 2013), and LILACs via BIREME Virtual Health Library (1980 to 22 October 2013). We applied no restrictions on language or date of publication when searching the electronic databases. We contacted manufacturers of dental materials to obtain any unpublished studies.

Selection criteria

Randomized controlled trials comparing dental resin composites with dental amalgams in permanent posterior teeth. We excluded studies having a follow-up period of less than three years.

Data collection and analysis

We used standard methodological procedures expected by The Cochrane Collaboration.

Main results

Of the 2205 retrieved references, we included seven trials (10 articles) in the systematic review. Two trials were parallel group studies involving 1645 composite restorations and 1365 amalgam restorations (921 children) in the analysis. The other five trials were split-mouth studies involving 1620 composite restorations and 570 amalgam restorations in an unclear number of children. Due to major problems with the reporting of the data for the five split-mouth trials, the primary analysis is based on the two parallel group trials. We judged all seven trials to be at high risk of bias and we analyzed 3265 composite restorations and 1935 amalgam restorations.

The parallel group trials indicated that resin restorations had a significantly higher risk of failure than amalgam restorations (risk ratio (RR) 1.89, 95% confidence interval (CI) 1.52 to 2.35, P value < 0.001 (fixed-effect model) (low-quality evidence)) and increased risk of secondary caries (RR 2.14, 95% CI 1.67 to 2.74, P value < 0.001 (low-quality evidence)) but no evidence of an increased risk of restoration fracture (RR 0.87, 95% CI 0.46 to 1.64, P value = 0.66 (moderate-quality evidence)). The results from the split-mouth trials were consistent with those of the parallel group trials.

Adverse effects of dental restorations were reported in two trials. The outcomes considered were neurobehavioral function, renal function, psychosocial function, and physical development. The investigators found no difference in adverse effects between composite and amalgam restorations. However, the results should be interpreted with caution as none of the outcomes were reported in more than one trial.

Authors' conclusions

There is low-quality evidence to suggest that resin composites lead to higher failure rates and risk of secondary caries than amalgam restorations. This review reinforces the benefit of amalgam restorations and the results are particularly useful in parts of the world where amalgam is still the material of choice to restore posterior teeth with proximal caries. The review found insufficient evidence to support or refute any adverse effects associated with amalgam or composite restorations. However, emerging research is highlighting issues around genetic susceptibility to mercury. The decision for a global phase-down of amalgam (Minamata Convention on Mercury) will restrict the future use of amalgam.

Résumé scientifique

Obturation directe en résine composite par rapport aux obturations en amalgame pour les dents postérieures permanentes ou adultes

Contexte

L'amalgame a été le matériau traditionnel d'obturation des cavités sur les dents postérieures durant ces 150 dernières années et, en raison de son efficacité et de son coût, l'amalgame est toujours le matériau de restauration de choix dans certaines parties du monde. Cependant, des inquiétudes ont dernièrement été formulées sur l'utilisation des restaurations (obturations) à base d'amalgame, relatives à la libération de mercure dans le corps et à l'impact de l'environnement suite à son élimination. Les composites en résine sont devenus une alternative esthétique aux restaurations en amalgame et une nette amélioration de ses propriétés mécaniques pour restaurer les dents postérieures a été constatée.

Il est nécessaire d'examiner les nouvelles preuves comparant l'efficacité des deux restaurations.

Objectifs

Examiner les effets des obturations en résine composite directe par rapport aux obturations en amalgame pour les dents permanentes postérieures, principalement sur l'échec de la restauration.

Stratégie de recherche documentaire

Nous avons effectué des recherches dans le registre des essais du groupe Cochrane sur la santé bucco-dentaire (jusqu'au 22 octobre 2013), le registre Cochrane des essais contrôlés (CENTRAL) (La Bibliothèque Cochrane 2013, numéro 9), MEDLINE via OVID (de 1946 au 22 octobre 2013), EMBASE via OVID (de 1980 au 22 octobre 2013) et LILACs via BIREME Virtual Health Library (de 1980 au 22 octobre 2013). Nous n'avons appliqué aucune restriction concernant la langue ou la date de publication lors des recherches dans les bases de données électroniques. Nous avons contacté les fabricants des matériaux dentaires pour obtenir toute étude non publiée.

Critères de sélection

Essais contrôlés randomisés comparant des composites dentaires en résine aux amalgames dentaires sur les dents permanentes postérieures. Nous avons exclu les études ayant une période de suivi de moins de trois ans.

Recueil et analyse des données

Nous avons utilisé des procédures méthodologiques standard prévues par la Collaboration Cochrane.

Résultats principaux

Sur les 2 205 références extraites, nous avons inclus sept essais (10 articles) dans la revue systématique. Deux essais étaient des études en groupes parallèles portant sur 1 645 restaurations en composite et 1 365 restaurations en amalgame (921 enfants) dans l'analyse. Les cinq autres essais étaient des études en bouche fractionnée portant sur 1 620 restaurations en composite et 570 restaurations en amalgame avec un nombre incertain d'enfants. En raison de graves problèmes de la notification des données pour les cinq essais en bouche fractionnée, l'analyse primaire est basée sur les deux essais en groupes parallèles. Nous avons jugé que tous les sept essais étaient à risque de biais élevé et nous avons analysé 3 265 restaurations en composite et 1 935 restaurations en amalgame.

Les essais en groupes parallèles indiquaient que les restaurations en résine présentaient un risque d'échec significativement plus élevé que les restaurations en amalgame (risque relatif (RR) 1,89, intervalle de confiance à 95 % (IC) de 1,52 à 2,35, valeur P < 0,001 (modèle à effets fixes) (preuves de faible qualité)) et un risque accru de caries secondaires (RR 2,14, IC à 95 % 1,67 à 2,74, valeur P < 0,001 (preuves de faible qualité)), mais ne présentaient aucune preuve d'un risque accru de fracture de la restauration (RR 0,87, IC à 95 % 0,46 à 1,64, valeur P = 0,66 (preuves de qualité modérée)). Les résultats des essais en bouche fractionnée étaient compatibles avec ceux des essais en groupes parallèles.

Les effets indésirables des restaurations dentaires ont été rapportés dans deux essais. Les critères de jugement considérés étaient la fonction neurocomportementale, la fonction rénale, la fonction psychosociale et le développement physique. Les investigateurs n'ont trouvé aucune différence concernant les effets indésirables entre les restaurations en composite et en amalgame. Cependant, les résultats doivent être interprétés avec prudence car seulement un essai rapportait les critères de jugement.

Conclusions des auteurs

Des preuves de qualité médiocre suggèrent que les composites en résine conduisent à un plus fort taux d'échec et de risque de caries secondaires comparés aux restaurations en amalgame. Cette revue renforce le bénéfice des restaurations en amalgame et les résultats sont particulièrement utiles dans les régions du monde où l'amalgame est encore le matériau de choix pour restaurer les dents postérieures atteintes d'une carie proximale. La revue n'a pas trouvé suffisamment de preuves pour soutenir ou réfuter tout effet indésirable associé aux restaurations en amalgame ou en composite. Cependant, les recherches émergentes mettent en lumière des problèmes liés à la sensibilité génétique au mercure. La décision pour la baisse progressive de l'utilisation de l'amalgame à l'échelle mondiale (Convention de Minamata sur le Mercure) en limitera l'utilisation future.

摘要

直接使用複合樹脂充填和汞齊充填作為恆久齒或成人後牙

背景

汞齊 (amalgam) 因為有效而且便宜,作為填補後牙蛀洞的傳統材料至少已有150年的歷史。目前世界上還有部分地區,仍然使用汞齊作為填補材料。不過近年來人們對於使用汞齊填補 (充填) 牙齒產生疑慮,因為使用汞齊不但可能在體內釋出汞,而且在丟棄時也會對環境造成影響。相較於汞齊填補,使用樹脂複合材料填補牙齒較為美觀,而且它的機械性質也已顯著改良,可以用來修補後牙。

必須回顧新的證據,比較兩種牙齒修復術的效果。

目的

檢視直接複合樹脂充填與汞齊充填恆久後牙的效果,主要針對修復術失敗。

搜尋策略

我們搜尋了考科藍口腔健康群組試驗註冊 (Cochrane Oral Health Group's Trials Register) (截至2013年10月22日為止)、考科藍對照試驗中央註冊 (Cochrane Central Register of Controlled Trials, CENTRAL) (考科藍圖書館,2013年第9次發行)、EMBASE via OVID (1980年至2013年10月22日),以及LILACs via BIREME Virtual Health Library (1980年至2013年10月22日)。在搜尋電子資料庫時,我們並未設定語言或出版日期限制。我們也聯絡牙科材料製造商,收集未發表的試驗資訊。

選擇標準

隨機對照試驗,比較牙齒複合樹脂和汞齊充填恆久後牙的效果。本次文獻回顧排除追蹤期不到3年的試驗。

資料收集與分析

本次文獻回顧採用考科藍合作組織 (Cochrane Collaboration) 所建議的標準方法學程序。

主要結果

本次系統性文獻回顧共計搜集2205項試驗,並納入7篇試驗 (10篇論文)。其中有2篇試驗為平行分組試驗,共有1645件複合物修復術與1365件汞齊修復術 (321名兒童) 納入分析。其他5篇試驗為分口 (split-mouth) 試驗,包含1620件複合物修復術與570件汞齊修復術,但病童數目不明。由於這5篇分口試驗所通報的資料有重大瑕疵,因此主要分析以2篇平行分組試驗為基礎。我們判定所有7篇試驗均具高偏差風險,本次文獻回顧共計分析3265件複合物修復術和1935件汞齊修復術。

平行分組試驗指出,樹脂修復術的失敗風險,顯著高於汞齊修復術 (風險比 [risk ratio, RR] 為1.89,95%信賴區間 [confidence interval, CI] 為1.52至2.35,P值< 0.001 [固定效果模式] [證據品質低]),而且發生續發性齲齒 (secondary caries) 的風險增加 (RR為2.14,95% CI為1.67至2.74,P值 < 0.001 [證據品質低]),但並無證據顯示補綴物斷裂的風險增加 (RR為0.87,95% CI為0.46至1.64,P值=0.66 [證據品質中等])。分口試驗的結果與平行分組試驗一致。

有2篇試驗提及牙科修復術的不良作用,考慮的結果包括神經行為功能、腎功能、心理社會功能和生理發展。試驗主持人發現,複合物和汞齊修復術的不良作用並無差異。不過必須謹慎解讀試驗結果,因為每項結果皆僅包含1項試驗。

作者結論

有品質偏低的證據顯示,複合樹脂修復術的失敗率和發生續發性齲齒的風險,高於汞齊修復術。本次文獻回顧突顯汞齊修復術的益處,這些結果對仍然使用汞齊修補後牙近側蛀牙的地區特別有助益。雖然本次文獻回顧所找到的證據,不足以支持或反駁汞齊產生的任何不良作用但新研究也不可能改變人們對於汞齊安全性的評價,以及全球逐漸減少使用汞齊的決定 (水俣公約 [Minamata Convention on Mercury]),對於汞齊安全性的普遍見解不可能改變。

譯註


翻譯者:臺北醫學大學實證醫學研究中心。
本翻譯計畫由衛生福利部補助經費,臺北醫學大學實證醫學研究中心、台灣實證醫學學會及東亞考科藍聯盟(EACA)統籌執行。

Plain language summary

Tooth-colored resin fillings compared with amalgam fillings for permanent teeth at the back of the mouth

Review question

This review, carried out by the Cochrane Oral Health Group, addressed the question of how effective tooth-colored (composite resin) fillings are compared with conventional amalgam fillings when placed directly into cavities in permanent teeth in the back of the mouth.

Background

There is controversy over the best materials to use when restoring or filling holes caused by tooth decay in permanent teeth at the back of the mouth. Amalgam fillings have been successfully used for over 150 years and are cost effective. However, their use has declined over recent years partly because of the way they look and because of the perceived risk of mercury that is used in them. Tooth-colored (composite resin) fillings are frequently used in the front teeth and also in permanent teeth at the back of the mouth.

Study characteristics

The evidence on which this review is based was up to date as of 22 October 2013. We searched scientific databases and found seven studies to include in this review comparing composite resin fillings with amalgam fillings and we included two of these studies in the main analysis. There were 3265 composite fillings and 1935 amalgam fillings but is unclear how many children these were in. The exact age of participants was also unclear in some studies; however, both children and adults with permanent teeth at the back of the mouth that required fillings were included. Study centers were located in the UK, USA, Portugal, Sweden, The Netherlands, Belgium, and Germany.

Key results

The main result including only two studies in 921 children suggests that amalgam fillings had lower failure rates than tooth-colored (composite resin) fillings used to fill holes caused by decay in permanent teeth at the back of the mouth. Further tooth decay (secondary caries) also occurred less frequently next to or under amalgam fillings compared with composite resin fillings. There was no evidence of a difference in the breaking of the two types of fillings.

The other five studies only reported the rate of failure of the fillings and the amount of further tooth decay occurring next to or under the fillings (secondary caries) and the results supported those of the two studies above.

The results suggest that tooth-colored (composite resin) fillings are almost twice as likely to fail compared with amalgam fillings when used for filling permanent teeth at the back of the mouth.

Quality of the evidence

The quality of the evidence was low to moderate. Because there was an obvious difference in the color of the fillings, it was not possible to do the comparisons 'blind' so there was, therefore, a high risk of bias.

Résumé simplifié

Obturations en résine de la couleur des dents par rapport aux obturations en amalgame pour les dents permanentes à l'arrière de la bouche

Question de la revue

Cette revue, réalisée par le groupe Cochrane sur la santé bucco-dentaire, a traité la question de l'efficacité des obturations de la couleur des dents (résines composites) comparée aux obturations conventionnelles en amalgame, lorsqu'elles sont placées directement dans les cavités des dents permanentes à l'arrière de la bouche.

Contexte

Les meilleurs matériaux d'obturation à utiliser lors de la restauration ou de l'obturation de trous causés par les caries dentaires dans les dents permanentes à l'arrière de la bouche sont sujets à controverse. Les obturations en amalgame ont été utilisées avec succès pendant plus de 150 ans et sont économiques. Toutefois, leur utilisation a décliné ces dernières années en partie en raison de leur apparence et du risque perçu de mercure utilisé. Les obturations de la couleur des dents (résines composites) sont fréquemment utilisées pour les dents de devant et également sur les dents permanentes à l'arrière de la bouche.

Les caractéristiques de l'étude

Les preuves sur lesquelles cette revue est basée étaient à jour le 22 octobre 2013. Nous avons effectué des recherches dans des bases de données scientifiques et nous avons trouvé sept études à inclure dans cette revue comparant les obturations en résine composite avec les obturations en amalgame et nous avons inclus deux de ces études dans l'analyse principale. Il y avait 3 265 obturations en composite et 1 935 obturations en amalgame, mais le nombre d'enfants était incertain. Dans plusieurs études, l'âge exact des participants était également incertain; toutefois, les enfants et les adultes, avec des dents permanentes à l'arrière de la bouche qui nécessitaient des obturations, ont été inclus. Les centres d'études se situaient au Royaume-Uni, aux États-Unis, au Portugal, en Suède, aux Pays-Bas, en Belgique et en Allemagne.

Résultats principaux

Le principal résultat, incluant seulement deux études chez 921 enfants, suggère que les obturations en amalgame avaient de plus faibles taux d'échec que les obturations de la couleur des dents (résines composites) utilisées pour combler les trous causés par des caries sur les dents permanentes à l'arrière de la bouche. D'autres formations de caries (caries secondaires) étaient également moins fréquentes à proximité ou sous les obturations en amalgame par rapport aux obturations en résine composite. Il n'y avait aucune preuve d'une différence au niveau de la rupture dans les deux types d'obturations.

Les cinq autres études n'ont rapporté que le taux d'échec des obturations et la quantité de récurrence d'une carie dentaire survenant à proximité ou sous les obturations (caries secondaires) et les résultats soutenaient ceux des deux études ci-dessus.

Les résultats suggèrent que les obturations de la couleur des dents (résines composites) sont presque deux fois plus susceptibles d'échouer par rapport aux obturations en amalgame lorsqu'ils sont utilisés pour combler les dents permanentes à l'arrière de la bouche.

Qualité des preuves

La qualité des preuves était de faible à modérée. Du fait d'une différence évidente dans la couleur des obturations, il n'était pas possible de réaliser des comparaisons « en aveugle », il y avait donc un risque de biais élevé.

Notes de traduction

Traduit par: French Cochrane Centre 22nd June, 2014

Laički sažetak

Smolasti materijali u boji zuba u usporedbi s amalgamskim ispunima (sive plombe) za trajne zube u stražnjim regijama usne šupljine

Istraživačko pitanje

Ovaj sustavni pregled izradila je Cochrane skupina za oralno zdravlje, a odgovara na pitanje o djelotvornosti ispuna u boji zuba (kompozitne smole) u usporedbi s uobičajenim amalgamskim ispunima, kada su postavljeni direktno u šupljine na stražnjim trajnim zubima.

Pozadina

Postoje kontroverze oko najboljeg materijala za restauraciju zuba ili zatvaranja šupljina uzrokovanih karijesom na trajnim stražnjim zubima. Amalgamski se ispuni uspješno i isplativo koriste preko 150 godina. No njihova je uporaba zadnjih nekoliko godina u opadanju, djelomično zbog estetike i mogućeg rizika od djelovanja žive koja se nalazi u njima. Ispuni u boji zuba (kompozitne smole) često se koriste kod prednjih, ali i i kod stražnjih trajnih zuba.

Značajke studija

Dokazi na kojima se temelji ovaj Cochrane sustavni pregled objavljeni su do 22. listopada 2013. godine. Pretražene su znanstvene baze podataka i nađeno sedam studija koje su uključene u ovaj sustavni pregled u kojemu se uspoređuju kompozitni s amalgamskim ispunima te su dvije od navedenih sedam studija uključene u glavnu analizu. U uključenim istraživanjima napravljeno je 3265 kompozitnih i 1935 amalgamskih ispuna, ali nije poznat broj djece uključene u analizu. Nije jasna ni točna dob ispitanika u nekim studijama; međutim, uključena su djeca i odrasle osobe kojima su bili potrebni ispuni na stražnjim trajnim zubima. Studije su bile provedene u Velikoj Britaniji, SAD-u, Portugalu, Švedskoj, Nizozemskoj, Belgiji i Njemačkoj.

Ključni rezultati

Glavni rezultat koji uključuje samo dvije studije s 921 djece pokazuje da su amalgami imali nižu stopu neuspjeha u usporedbi s ispunima u boji zuba (kompozitni ispuni) koji su korišteni za zatvaranje šupljina uzrokovanih karijesom na stražnjim trajnim zubima. Sekundarni se karijes rjeđe pojavljivao uz ili ispod amalgamskih u usporedbi sa kompozitnim ispunima. Nisu nađeni dokazi o razlici u stopi pucanja te dvije vrste ispuna.

Ostalih pet studija je samo pokazalo stupanj neuspjeha ispuna i količinu sekundarnog karijesa koji nastaje uz ili ispod ispuna, a njihovi rezultati potkrepljuju dvije prethodno navedene studije.

Prema ovim rezultatima, materijali u boji zuba (kompozitni ispuni) imaju dvostruko veću mogućnost neuspjeha u usporedbi s amalgamskim ispunima kada se koriste na stražnjim trajnim zubima.

Kvaliteta dokaza

Kvaliteta dokaza bila je niska do srednja. Nije bilo moguće napraviti „slijepi“ test jer postoji očita razlika u boji ispuna, pa je rizik od pristranosti bio velik.

Bilješke prijevoda

Hrvatski Cochrane ogranak.
Prevela: Andrea Hoch

淺顯易懂的口語結論

口腔後方恆久齒的天然色樹脂充填與汞齊充填

回顧問題

本次文獻回顧由考科藍口腔健康群組 (Cochrane Oral Health Group) 負責進行,針對直接填補口腔後方恆久齒蛀牙的狀況,探討天然色 (複合樹脂) 充填和傳統汞齊充填的效果。

背景

人們對於用來修復或充填口腔後方恆久齒蛀洞的最佳材料,始終有爭議。汞齊充填已成功使用超過150年,而且具有成本效益。不過近年來汞齊的使用率下降,部分由於外觀,部分則是起因於人們意識到使用汞齊可能有釋出汞的風險。天然色 (複合樹脂) 材料通常用來填補前牙,但也可以用來填補口腔後方的恆久齒。

試驗特色

本次文獻回顧立基於截至2013年10月22日為止的最新證據。我們搜尋科學資料庫,並將7篇試驗納入本次文獻回顧,比較複合樹脂充填和汞齊充填的效果,其中有2篇試驗納入主要分析。本次文獻回顧共計分析3265件複合物充填和1935件汞齊充填修復術,但不清楚接受治療的兒童人數。部分試驗並未明確提及受試者的年齡,不過包含口腔後方恆久齒需要填補的兒童和成人患者。試驗中心位於英國、美國、葡萄牙、瑞典、荷蘭、比利時和德國。

重要結果

主要結果僅納入2篇試驗,收錄921名兒童,分析結果顯示在填補口腔後方恆久齒的蛀洞時,汞齊充填的失敗率低於天然色 (複合樹脂) 充填。相較於複合樹脂充填,汞齊充填後未來的齲齒 (續發性齲齒) 發生率也較低。並無證據顯示兩種充填材料的斷裂狀況有差異。

其他5篇試驗僅提及充填的失敗率,和填補處旁邊或下方未來發生齲齒 (續發性齲齒) 的數量。

此5篇試驗的結果,支持上述2篇試驗結果。分析結果顯示,當用於填補口腔後方恆久齒時,天然色 (複合樹脂) 充填的失敗率,幾乎為汞齊充填的2倍。

證據品質

證據品質偏低或中等。因為充填物的顏色具有明顯差異,無法進行「盲性」比較,因此具有高度的偏差風險。

譯註


翻譯者:臺北醫學大學實證醫學研究中心。
本翻譯計畫由衛生福利部補助經費,臺北醫學大學實證醫學研究中心、台灣實證醫學學會及東亞考科藍聯盟(EACA)統籌執行。

Summary of findings(Explanation)

Summary of findings for the main comparison. Primary and secondary outcomes for permanent or adult posterior teeth
  1. 1 Performance, detection, and selection (due to allocation concealment) bias2 I2 = 87%3 I2 = 92%
    4 Imprecision

Primary and secondary outcomes for permanent or adult posterior teeth

Patient or population: people with permanent or adult posterior teeth
Settings: outpatients
Intervention: composite

Control: amalgam

OutcomesIllustrative comparative risks* (95% CI)Relative effect
(95% CI)
No of teeth
(studies)
Quality of the evidence
(GRADE)
Comments
Assumed riskCorresponding risk
AmalgamComposite
Failure rate
Follow-up: 5-7 years
75 per 1000 142 per 1000
(114 to 176)
RR 1.89
(1.52 to 2.35)
3010
(2 studies)
⊕⊕⊝⊝
low 1,2
Reasons for failure include secondary caries, fracture, restoration loss
Secondary caries
Follow-up: 5-7 years
57 per 1000 122 per 1000
(95 to 156)
RR 2.14
(1.67 to 2.74)
3010
(2 studies)
⊕⊕⊝⊝
low 1,3
None
Fracture of restorations
Follow-up: 5-7 years
14 per 1000 12 per 1000
(6 to 23)
RR 0.87
(0.46 to 1.64)
3010
(2 studies)
⊕⊕⊝⊝
low 1,4
None
Adverse events See comments  Data were reported for neurobehavioral assessment, kidney function, psychosocial function, physical development. None of these outcomes were reported in more than 1 study. Evidence was insufficient to reach conclusions
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).
CI: confidence interval; RR: risk ratio.
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect.
Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate.
Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate.
Very low quality: We are very uncertain about the estimate.

Background

Description of the condition

Dental caries (tooth decay) is a dynamic and continuous process composed of cycles of demineralization of the hard tissue of the teeth followed by cycles of remineralization. The balance between the two cycles determines the stage of the disease (ICDAS 2011). There is a close relationship between oral health and quality of life just as socioeconomic status and home environment have been shown to impact on people's oral condition (Gomes 2009; Paula 2012). Despite the great accomplishments obtained globally in oral health, caries is still a serious problem particularly among under-privileged groups in low, middle and high-income countries, affecting 60% to 90% of school children and the vast majority of adults (Costa 2012). It is also the most prevalent oral health problem in several Asian and Latin-American countries (WHO 2012).

Modern management of dental caries involves making a diagnosis to determine the person's caries risk status, followed by the application of intervention strategies focused on preventing, arresting, and possibly reversing the caries process to delay restorative treatment until it becomes absolutely necessary (Ferreira Zandona 2012). When the damage on the tooth structure is permanent, the most commonly used treatment involves cleaning the cavity and filling it with a restorative material to restore the shape and function of the tooth.

Primary caries seems to be the most frequent reason for the placement of restorations (fillings) and caries lesions are most commonly found on occlusal surfaces of posterior teeth (Nascimento 2010). Secondary caries is responsible for 60% of all replacement restorations in the typical dental practice but the association between the type of restoration materials and location of caries and the composition of the microflora has not been found to be statistically significant (Mo 2010).

Description of the intervention

The obturation and filling of occlusal cavities is an issue that has been long studied. The choice of the best material for restoring the anatomical structures that also achieves acceptable resistance to the forces of mastication is still controversial. This review compared dental amalgams and resin composites, the two main categories of dental restorative fillings used in posterior tooth restorations today.

Dental amalgams are metallic alloys. They have been predictable and inexpensive restorative materials for over 150 years. Their use and success rate have been well documented and they are the most cost-effective materials in posterior teeth restorations. However, they are declining in use in dentistry mainly due to their unesthetic appearance and concerns about their mercury content (Kelly 2004; Mitchell 2007; Roulet 1997).

Dental resin composites were developed in response to people's demands for tooth-colored restorations. Dental resin composites are particle-reinforced resins. The indications of resin composites have expanded from anterior teeth to restrict posterior restorations and even to stress-bearing posterior restorations as amalgam substitutes or amalgam alternatives (Lutz 1999). Other advantages of dental resin composite restorations include their conservative design and reparability.

The cost of placing dental amalgams (USD 12.40) is only slightly cheaper than the cost of placing composite fillings (USD 15.90) for a single restoration provided in one dental session. However, when the costs are considered in the long term, taking into consideration the differences in longevity of the two materials, Sjögren et al. calculated that the estimated cost over 10 years for a Class II restoration was USD 189.80 for amalgam fillings and USD 363.70 for a composite filling (CADTH 2012).

How the intervention might work

Dental amalgam and resin composite restorations are still the most current selection for restoring permanent molar and premolar cavities. The choice of amalgam as the preferred material to restore posterior teeth has been gradually replaced by resin composite. However, surveys and retrospective studies developed by groups of practice-based researchers differ in their conclusions about which is the material most commonly used in restorative dentistry today (Makhija 2011; Nascimento 2010).

In recent years, the field of composite dental restoratives continues to propose and achieve significant and exciting advances in resin formulation, filler loading and modification, and curing methodologies and mechanisms (Cramer 2011).

The current controversy is that amalgam restorations should be banned because of mercury toxicity. In addressing safety concerns, it is important to make the distinction between known and hypothetical risks (Rathore 2012). The truth is that a variety of potentially toxic compounds might be released from restorative dental materials (amalgam and composites) and can diffuse into the tooth pulp or gingiva reaching both saliva and circulating blood (Libonati 2011). Their adverse effects are not yet well known.

Why it is important to do this review

While the use of dental amalgam has declined (Mitchell 2007) in some parts of the world, it is still the restorative material of choice in other parts of the world. The decline is due to concerns about its mercury release in the body and environmental impact following its disposal. To achieve a balance between the environment impact of the disposal of mercury products including amalgam and its public health benefit, the Minamata Convention on Mercury proposes a paced phase-down by national governments according to local needs (BDA 2013; UNEP 2013). The World Health Organization (WHO) further iterates that the move from amalgam would depend on quality improvement of alternative restoration materials. Since the adhesive dentistry remains one of the fastest changing fields and will most likely continue well into the next decade (McDonald 2001), there is need to provide a comprehensive update on the effects of composite materials in comparison with amalgam.

Objectives

To examine the effects of direct composite resin fillings versus amalgam fillings for permanent posterior teeth, primarily on restoration failure.

Methods

Criteria for considering studies for this review

Types of studies

All randomized controlled trials comparing dental resin composites with dental amalgams in permanent posterior teeth (dating back to 1946) were selected, including studies with parallel group or split-mouth designs. We excluded studies that had less than a three-year follow-up period.

Types of participants

Adults or children with permanent posterior teeth suitable (i.e. with tooth decay) for resin composite or amalgam restorations or both.

Types of interventions

  • Intervention: dental resin composites.

  • Control: dental amalgams.

Types of outcome measures

Primary outcomes
  • Failure rate (or survival rate) of the restorations.

Secondary outcomes
  • Reasons for failure (according to the evaluation categories of the United States Public Health Service (USPHS), which includes color match, marginal adaptation, anatomical form, and secondary caries) and patient satisfaction. The minimum length of follow-up that was acceptable for outcomes was three years.

  • Cost data (treatment time plus material costs).

  • Unexpected/adverse events (as reported in included trials).

Search methods for identification of studies

Electronic searches

For the identification of studies included in, or considered for this review, we developed detailed search strategies for each database searched. We based these on the search strategy developed for MEDLINE (OVID) but revised appropriately for each database.

We searched the following electronic databases:

  • the Cochrane Oral Health Group's Trials Register (to 22 October 2013) (Appendix 1);

  • the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2013, Issue 9) (Appendix 2);

  • MEDLINE via OVID (1946 to 22 October 2013) (Appendix 3);

  • EMBASE via OVID (1980 to 22 October 2013) (Appendix 4);

  • LILACS via BIREME Virtual Health Library (1980 to 22 October 2013) (Appendix 5).

Searching other resources

Handsearching for this review was done as part of the Cochrane worldwide handsearching program, see the Cochrane Master List for details of the journals and issues searched to date. We checked the reference lists of all eligible trials and relevant review articles for additional studies.

We contacted the authors of unpublished studies, but did not receive any replies.

We contacted the major manufacturers of dental materials (GC and 3M ESPE) in June 2012 to obtain information on published and unpublished trials/studies that may have involved their products. We were informed that no studies comparing resin composite materials and amalgam materials had been carried out. We also contacted Ivoclar Vivident, Kerr and Dentsply at the same time but they did not reply.

Language

We placed no restrictions on language or date of publication in the databases searched.

Data collection and analysis

Selection of studies

Review authors, working independently and in duplicate, assessed the titles and abstracts resulting from the searches to identify eligible studies for this review. We obtained the full copies of possible studies and assessed them to see if they met the inclusion criteria. We directed studies on which agreement was not reached to two other review authors who also worked independently. We excluded studies until further clarification was available or if we were unable to reach a consensus. We tabulated excluded studies with reasons for exclusion (Characteristics of excluded studies table). We resolved disagreements by discussion.

Data extraction and management

The four review authors piloted specially designed data extraction forms on two papers and modified the forms before use. We resolved any disagreements by discussion. Two review authors extracted data independently and in duplicate from each study that was relevant to the specified outcomes, and sent the data forms to the other two review authors for comparison and verification.

The features of the studies that we reported in the Characteristics of included studies table in the review were as follows:

  1. methods - unit of randomization (participants or teeth), exclusions after randomization, unusual study design, practice setting;

  2. participants - country and date of the trial, number randomized, main inclusion and exclusion criteria, losses to follow-up, stratification by age, sex, tooth type (location of the restoration), surfaces of restoration (type of cavity);

  3. interventions - materials used in treatment, comparison intervention (control);

  4. outcomes - failure rate (or survival rate) of the resin composite or dental amalgam restorations over time (yearly beginning from three years) with failure defined as the rating of the clinical performance greater than bravo using the assessment criteria of the USPHS guidelines, reasons of failure (secondary caries), fracture of the restoration;

  5. notes - additional details relevant to that particular trial (e.g. funding sources).

Assessment of risk of bias in included studies

Two review authors undertook the assessment of risk of bias independently and in duplicate for each included study using the Cochrane 'Risk of bias' assessment tool (Higgins 2011). We assessed seven domains for each included study: sequence generation (selection bias), allocation sequence concealment (selection bias), blinding of participants and personnel (performance bias), blinding of outcome assessment (detection bias), incomplete outcome data (attrition bias), selective outcome reporting (reporting bias), and other potential sources of bias. The risk of bias was assessed as 'low risk', 'high risk', or 'unclear risk', with the last category indicating either lack of information or uncertainty over the potential for bias.

The Cochrane Collaboration's tool for assessing risk of bias
Domain Support for judgment Review authors' judgment
Selection bias.  
Random sequence generation.Describe the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.Selection bias (biased allocation to interventions) due to inadequate generation of a randomized sequence.
Allocation concealment.Describe the method used to conceal the allocation sequence in sufficient detail to determine whether intervention allocations could have been foreseen in advance of, or during, enrolment.Selection bias (biased allocation to interventions) due to inadequate concealment of allocations prior to assignment.
Performance bias.  

Blinding of participants and personnel 

Assessments should be made for each main outcome (or class of outcomes).

Describe all measures used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective.Performance bias due to knowledge of the allocated interventions by participants and personnel during the study.
Detection bias.  
Blinding of outcome assessment Assessments should be made for each main outcome (or class of outcomes).Describe all measures used, if any, to blind outcome assessors from knowledge of which intervention a participant received. Provide any information relating to whether the intended blinding was effective.Detection bias due to knowledge of the allocated interventions by outcome assessors.
Attrition bias.  
Incomplete outcome data Assessments should be made for each main outcome (or class of outcomes).  Describe the completeness of outcome data for each main outcome, including attrition and exclusions from the analysis. State whether attrition and exclusions were reported, the numbers in each intervention group (compared with total randomized participants), reasons for attrition/exclusions where reported, and any re-inclusions in analyses performed by the review authors.Attrition bias due to amount, nature, or handling of incomplete outcome data.
Reporting bias.  
Selective reporting.State how the possibility of selective outcome reporting was examined by the review authors, and what was found.Reporting bias due to selective outcome reporting.
Other bias.  
Other sources of bias.

State any important concerns about bias not addressed in the other domains in the tool.

If particular questions/entries were pre-specified in the review's protocol, responses should be provided for each question/entry.

Bias due to problems not covered elsewhere in the table.

After taking into account the additional information provided by the authors of the trials, we grouped the studies into the following categories:

  1. low risk of bias (plausible bias unlikely to seriously alter the results);

  2. unclear risk of bias if one or more of the domains are assessed as unclear;

  3. high risk of bias (plausible bias that weakens confidence in the results) if one or more domains are assessed at high risk of bias.

Measures of treatment effect

For each trial, we calculated risk ratios (RR) with 95% confidence intervals (CI) for all pre-specified, dichotomous outcomes. We calculated mean difference (MD) or standardized mean difference (SMD) for continuous data. In the case of split-mouth design studies, we aimed to calculate log risk ratio separately for each outcome.

We aimed to extract time-to-event data from each study in our review, if possible, and to express the treatment effect as a hazard ratio using survival analysis. If necessary, outcome data would have been transformed to achieve consistency of results (e.g. calculate survival rate as dichotomous data from time-to-event data at fixed time points).

Unit of analysis issues

The unit of analysis was restoration. Whenever possible, we checked the included studies for unit of analysis errors and handled if considered appropriate following the advice provided in Section 16.3 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011).

Dealing with missing data

In case of missing individual data, we analyzed only available data. We performed an intention-to-treat (ITT) analysis if possible. In some cases, we contacted study authors when there was need for more information. We addressed the potential impacts of missing data on the findings of the review in the Discussion section.

Assessment of heterogeneity

We assessed heterogeneity by analyzing the point estimates and CIs on the forest plots. We assessed statistical heterogeneity using The Cochrane Collaboration's test for heterogeneity and quantified using the I2 statistic. According to the Cochrane Handbook for Systematic Reviews of Intervention, I2 values of 0% to 40% might not be important, 30% to 60% may represent moderate heterogeneity, 50% to 90% may represent substantial heterogeneity, and 75% to 100% is considerable heterogeneity (Higgins 2011). Heterogeneity was considered statistically significant if the P value was < 0.1.

Assessment of reporting biases

Only a proportion of research projects conducted are ultimately published in an indexed journal and become easily identifiable for inclusion in systematic reviews (Easterbrook 1991). Reporting biases arise when the reporting of research findings is influenced by the nature and direction of the findings of the research. We attempted to avoid time lag bias, multiple (duplicate) publication bias, and language bias by conducting a detailed sensitive search, including searching for ongoing studies. We did not restrict the search by language and non-English studies were translated by co-review authors due to their multinationality.

Data synthesis

We combined RRs for dichotomous data of the studies that were considered appropriate to be included in the meta-analysis. We intended to combine the treatment effects from split-mouth trials with those from parallel group trials where appropriate as outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Elbourne 2002; Higgins 2011), but it was not possible because of poor reporting. Therefore, we treated the split-mouth trials as a subgroup so that the results could be examined either in isolation or in combination with the parallel group studies. This was particularly aimed at providing a broader view and 'bottom-line' to the review question. We used random-effects models where there were more than three studies in any meta-analysis, otherwise we used fixed-effect models.

Subgroup analysis and investigation of heterogeneity

We intended to explore the following potential sources of heterogeneity using subgroup analyses:

  1. age of participants;

  2. location of restoration (premolar or molar);

  3. type of cavity (class I or II; stress bearing or not);

  4. materials used;

  5. practice setting (university based or private practice based) and operator.

However, there was not enough data available to explore the reasons of heterogeneity.

Sensitivity analysis

A sensitivity analysis was planned to examine the robustness of the meta-analysis but the number of included studies was inadequate.

Presentation of main results

We have presented a 'Summary of findings' table to show the findings of the most important outcomes (Summary of findings for the main comparison). We assessed the quality of the body of evidence by following the GRADE framework with reference to the overall risk of bias of the included studies, directness of the evidence, inconsistency of the results, precision of the estimates, risk of publication bias, and magnitude of the effect. We categorized the quality of the body of evidence for each of the outcomes as high, moderate, low, or very low.

Results

Description of studies

Results of the search

The search strategy retrieved 2205 references to studies after de-duplication. After examination of the titles and abstracts of these references, we considered 51 studies (54 articles) for critical appraisal. After evaluation of the full-text copies of the remaining studies, seven studies (10 articles) fulfilled the inclusion criteria.

A PRISMA flow diagram illustrates the results of the search, screening, and selection of studies for inclusion (Figure 1).

Figure 1.

PRISMA flow diagram of study inclusion.

Included studies

The articles obtained by bibliographic search were mostly in English and a minor proportion in German, Spanish, and Portuguese. Since the review authors were from different countries, they were able to read and translate the non-English studies. To obtain the full articles, we contacted different libraries and universities were contacted.

Characteristics of the trial designs

Seven randomized controlled trials (RCTs) that met the inclusion criteria were reported in 10 articles (Casa Pia 2007; Cunningham 1990; Hendriks 1986; Letzel 1989; NECAT 2007; Norman 1990; Robinson 1988). Two of the seven studies were parallel group trials (Casa Pia 2007; NECAT 2007), while the other five were split-mouth studies (Cunningham 1990; Hendriks 1986; Letzel 1989; Norman 1990; Robinson 1988).

The two parallel group studies reported data on two large RCTs that were developed to compare amalgam with composite to restore posterior teeth: The Casa Pia Study of Health Effects of Dental Amalgam in Children started in 1996 and was followed up for seven years (Casa Pia 2007), and The New England Children’s Amalgam Trial (NECAT) conducted between September 1997 and March 2005 (NECAT 2007).

Some of the split-mouth studies reported data from a multicenter RCT designed for testing resin composite materials as a material suitable to restore posterior teeth, using amalgam restorations as positive control. The data from the split-mouth studies were not reported or analyzed in an appropriate way taking the clustering of the sites within participants into account. There were different numbers in the two groups, which makes the analysis even more problematic.

Two studies were conducted in the UK (Cunningham 1990; Robinson 1988), one in Portugal (Casa Pia 2007), one in the USA (NECAT 2007), one was a multicenter trial conducted in parts of Europe and in the USA (Letzel 1989), and the locations of two studies were not clearly reported (Hendriks 1986; Norman 1990). Three studies were funded by the same dental industry (Letzel 1989; Norman 1990; Robinson 1988), one was funded by a research grant (Casa Pia 2007), and the other three studies did not state their funding sources (Cunningham 1990; Hendriks 1986; NECAT 2007).

Characteristics of the participants

Of the 1006 participants who took part in the two parallel group trials, data from 871 participants were analyzed. The participants were aged six to 12 years at baseline and follow-up period was five to seven years. Most of the split-mouth trials did not specify the number of participants recruited but reported data on 2190 restorations. The number of restorations varied between the five trials and ranged from 27 to 932.

Characteristics of the interventions

In the included studies, participants received amalgam restoration or composite resin restoration. In one study, participants received amalgam, compomer, or composite restoration but we have not presented the data on compomer restoration in this review (NECAT 2007).

Characteristics of outcomes

The primary outcome was failure rate. This parameter was collected and reported in all the included studies. Secondary caries was reported in six studies (Casa Pia 2007; Cunningham 1990; Hendriks 1986; NECAT 2007; Norman 1990; Robinson 1988), while fracture outcome data were reported in only two studies (Casa Pia 2007; NECAT 2007). Data on adverse outcomes were collected from participants included in the Casa Pia study and NECAT study but reported in three other articles linked to the respective primary studies. Neurobehavioral and renal function were reported in Casa Pia 2007, and psychosocial function and physical development were reported in NECAT 2007.

See Characteristics of included studies table for more information on included studies.

Excluded studies

See Characteristics of excluded studies table for further information on each excluded study.

In summary, the main reasons for exclusion after the critical appraisal of the 44 studies that had been initially identified as eligible for this review were:

Risk of bias in included studies

We judged all the included studies to be at high risk of bias (Figure 2). In most of the studies, bias was mainly due to lack of blinding. For the split-mouth studies in particular, it was due to failure to take clustering effect into account in the analysis.

Figure 2.

Risk of bias summary: review authors' judgments about each risk of bias item for each included study.

Randomization (selection bias)

We considered three studies to be at low risk of selection bias (NECAT 2007; Norman 1990; Robinson 1988), while the other four studies were at unclear risk of bias for poor details on randomization process (Casa Pia 2007; Cunningham 1990; Hendriks 1986; Letzel 1989).

Allocation

In all the included studies, there was no indication of allocation concealment. However, we judged the five split-mouth studies to be at low risk of bias because a lack of allocation concealment would neither make a difference nor introduce bias to a split-mouth study (Cunningham 1990; Hendriks 1986; Letzel 1989; Norman 1990; Robinson 1988). We considered the two parallel studies to be at high risk of bias (Casa Pia 2007; NECAT 2007).

Blinding

We found all the studies to be at high risk of performance bias and detection bias since the nature of the intervention (dental restorations) does not allow blinding for the operators or for the participants. Even though some studies indicated that outcome assessment was carried out by evaluators independent of the operators (Norman 1990; Robinson 1988), we did not consider this to be sufficient to minimize detection bias.

Incomplete outcome data

Drop-out rates were similar in the intervention and comparator groups in the two studies we judged to be at low risk of attrition bias (Casa Pia 2007; NECAT 2007). In the other five studies that we considered to be at unclear risk of bias, an overall drop-out rate was reported (Cunningham 1990; Hendriks 1986; Letzel 1989; Norman 1990; Robinson 1988). However, we were unable to determine whether the drop-out rate was differential.

Selective reporting

The data were well documented in all but one study (Letzel 1989), which reported all data for composite resin but did not report all the amalgam data.

Other potential sources of bias

None of the split-mouth studies had clearly indicated the number of restorations per participant resulting in high risk of bias due to unit of analysis error (Cunningham 1990; Hendriks 1986; Letzel 1989; Norman 1990; Robinson 1988). In addition, Letzel 1989 reported that there were notable variations in results across the different centers involved in the trial but provided no explanation for this. The two studies that we judged to be at low risk had no other apparent biases (Casa Pia 2007; NECAT 2007).

Effects of interventions

See: Summary of findings for the main comparison Primary and secondary outcomes for permanent or adult posterior teeth

Due to the poor reporting of the split-mouth studies, which makes the reported data unreliable, we decided that the primary analysis should only include the two parallel group studies. We also undertook a secondary analysis of all included trials. We studied failure rate as the primary outcome, and secondary caries and fracture of the restoration as secondary outcomes. Psychosocial function, physical development, neurobehavioral assessments, and kidney function were considered to explore adverse effects of mercury release.

Failure rate

The parallel group trials both recorded failure rate in the amalgam and composite group over a period of five to seven years. In total, 1365 amalgam restorations and 1645 composite restorations were analyzed. The pooled estimate showed that composite restorations had a significantly higher risk of failure than amalgam (risk ratio (RR) 1.89, 95% confidence interval (CI) 1.52 to 2.35, P value < 0.001; fixed-effect model) (Analysis 1.1). There was indication of heterogeneity (P value = 0.005; I2 = 87%), but, as there were only two studies, this could not be investigated. As the effect estimates for both studies were in the same direction, we decided to undertake the meta-analysis.

A subgroup analysis of the split-mouth studies also showed a similar trend with composite restorations having a higher risk of failure than amalgam restorations (RR 1.33, 95% CI 0.84 to 2.11, P value = 0.23; random-effects model) (note fixed-effect model displayed in forest plot as primary result is for parallel group subgroup). There was no evidence of heterogeneity (P value = 0.57; I2 = 0%).

There was no evidence of a difference between the study design subgroups and the results of the parallel group and split-mouth trials when combined showed more precise results with composite restorations having a significantly higher risk of failure than amalgam restorations (RR 1.62, 95% CI 1.13 to 2.4, P value = 0.009; random-effects model). There was some evidence of heterogeneity (P value = 0.05; I2 = 52%).

Secondary caries

Secondary caries was the most common reason for failure in the included studies. Meta-analysis of the parallel group studies showed a higher risk of secondary caries in permanent posterior teeth with composite restoration compared with teeth with amalgam restoration (RR 2.14, 95% CI 1.67 to 2.74, P value < 0.001; fixed-effect model) (Analysis 1.2). Once again there was evidence of heterogeneity (P value < 0.001; I2 = 92%), but, as there were only two studies, this could not be investigated. As the effect estimates for both studies were in the same direction, we decided to undertake the meta-analysis.

The outcome data from the split-mouth studies showed no significant difference in secondary caries when composite restorations were compared with amalgam restorations (RR 1.3, 95% CI 0.34 to 4.97, P value = 0.7; random-effects model). There was no evidence of heterogeneity (P value = 0.64; I2 = 0%).

The combined results of the parallel group and split-mouth trials indicated an increased risk of secondary caries for composite restorations (RR 1.93, 95% CI 0.98 to 3.80, P value = 0.06; random-effects model). There was some evidence of heterogeneity (P value = 0.02; I2 = 64%).

Fracture of the restoration

Fracture of the restorations does not seem to be a common reason for failure in the studies reporting data on fracture. There was no evidence of a difference in risk of fracture between the two materials (RR 0.87, 95% CI 0.46 to 1.64, P value = 0.66; fixed-effect model). There was no evidence of heterogeneity (P value = 0.44; I2 = 0%).

Analysis of subgroups

One study reported failure rates separately in molars and premolars (Casa Pia 2007), but the results were not sufficient to determine whether there was an association between location of the restorations in different teeth and failure rate of restorations.

Adverse effects

Casa Pia 2007 presented trial results on the effects of mercury on the nervous system and the potential damage to the renal system in children. Some tests were carried out at baseline and at seven years after a filling placement, to explore intelligence, nerve conduction velocity, memory, attention, and visuomotor function (Additional Table 1). To study renal function, creatinine-adjusted urinary albumin levels were recorded at years one, two, three, four, five, six, and seven (Additional Table 2). According to the results, there was no statistically significant differences in measures of memory, attention, visuomotor function, or nerve conduction velocities. There were no significant group differences in creatinine-adjusted urinary albumin over the seven years of follow-up. A re-analysis of the data published in 2011, based on amalgam size and years of exposure, found a significant association between amalgam and the porphyrin biomarkers for mercury-related enzyme blockage, which suggests amalgams are a significant contributor to mercury body burden. A further investigation of a subgroup of children with genotyping assays demonstrated a genetic susceptibility to the adverse neurobehavioral effects of mercury exposure in children, predominantly in boys.

Table 1. Neurobehavioral assessment
  1. CTONI: Comprehensive Test of Non-verbal Intelligence; RAVLT: Rey Auditory Verbal Learning Test; SD: standard deviation; WRAVMA: Wide Range Assessment of Visual Motor Abilities; WAIS-III: Wechsler Adult Intelligence Scale - Third Edition; WRAML: Wide Range Assessment of Memory and Learning; WASI: Wechsler Abbreviated Scale of Intelligence; WMS-III: Wechsler Memory Scale - Third Edition.

MEMORY
Method of measurement - RAVLT memory test
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment2548.13.72548.362.91
At 7 years1769.732.791729.652.86
Method of measurement - WRAML visual memory (1) WMS-III reproductions delayed (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)2546.523.122536.563.04
At 7 years (2)17632.986.2417233.026.24
Method of measurement - WRAMLS visual learning (1) WMS-III reproductions immediate (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)2548.142.752537.832.64
At 7 years (2)17635.793.6817235.154.47
Method of measurement - RAVLT total learning test
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25437.959.6125339.099.98
At 7 years17647.369.4817246.069.09
ATTENTION/CONCENTRATION
Method of measurement - Coding (1) WAIS-III digit symbol (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)2548.643.142539.043.14
At 7 years (2)1769.452.981729.452.86
Method of measurement - Symbol search (1) WAIS-III symbol search (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)2549.412.592539.392.69
At 7 years (2)1769.402.851729.773.08
Method of measurement - Digit span (1) WAIS-III digit span (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)2547.372.532537.42.73
At 7 years (2)1767.642.171727.702.21
Method of measurement - Finger windows (1) WAIS-III spatial span (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)2547.282.472537.322.35
At 7 years (2)1769.032.961729.342.99
Method of measurement - Trial A, seconds (1) Adult Trial A, seconds (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)25427.6913.0525327.9512.74
At 7 years (2)17628.9412.0617228.7211.26
Method of measurement - Trial B, seconds (1) Adult Trial B, seconds (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)25465.135.6125342.186.56
At 7 years (2)17663.8425.517265.3425.07
Method of measurement - Stroop word
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25441.546.3925342.186.56
At 7 years17641.78.0917241.418.04
Method of measurement - Stroop color
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25443.035.6225344.156.01
At 7 years17641.598.1617242.678.14
Method of measurement - Stroop color-word
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25443.36.8425344.176.93
At 7 years17646.999.7117248.429.41
VISUOMOTOR
Method of measurement - WRAVMA matching (1) WASI matrices (2)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment (1)25496.1912.425395.5713.72
At 7 years (2)17624.445.3317224.835.02
Method of measurement - WRAVMA pegs (dominant)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment254103.0416.68253101.9416.87
At 7 years176119.3815.83172119.0115.55
Method of measurement - WRAVMA pegs (non-dominant)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment254106.8115.03253106.1814.64
At 7 years176119.3815.83172119.0115.55
Method of measurement - Standard reaction time
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment2540.90.22530.90.2
At 7 years1760.760.141720.770.15
Method of measurement - Finger tapping (dominant)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25436.296.0525336.666.17
At 7 years17650.56.5617250.516.56
Method of measurement - Finger tapping (non-dominant)
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25431.335.3725332.025.34
At 7 years17644.496.3317244.486.34
NERVE CONDUCTION VELOCITY
Method of measurement - Tibial, m/s
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25451.585.5825351.125.29
At 7 years14050.155.0914050.785.07
Method of measurement - Ulnar, m/s
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25458.756.5125359.576.39
At 7 years14057.586.5214059.266.41
INTELLIGENCE
Method of measurement - CTONI
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment25485102538510
At 7 years17681121738112
Method of measurement - WASI
 Resin compositeAmalgam
 nMeanSDnMeanSD
At treatment254NA 253NA 
At 7 years17692131739414
Table 2. Kidney function
  1. CI: confidence interval.

Secondary outcome - kidney function
Creatinine-adjusted urinary albumin levels
  Composite Amalgam
 Mean95% CIMean95% CI
Year 17.44.2 to 12.57.73.1 to 11.5
Year 29.45.3 to 16.18.65.5 to 13.4
Year 39.96.8 to 16.79.05.5 to 17.9
Year 49.255.8 to 20.88.75.6 to 14.5
Year 58.25.1 to 14.38.05.4 to 12.5
Year 67.54.8 to 14.37.34.8 to 14.0
Year 76.84.4 to 13.76.54.3 to 12.3

The NECAT 2007 trial focused on the effect of restorations on psychosocial function (Additional Table 3) and physical development (Additional Table 4) in children after five years of follow-up. The effect of restorations on psychosocial function was measured using two validated instruments: Child Behavior Checklist (CBCL) parent report and Behaviour Assessment for Children Self Report (BASC-SR). The degree of exposure to restorations was expressed in surface years (SY); however, no direct comparison was made between children in the composite and amalgam arm. The BASC-SR measured emotional symptoms, clinical maladjustment, school maladjustment, personal adjustment, and core syndromes such as anxiety, depression, attitude to school, and interpersonal relations. The CBCL measured competence, total problem behaviors, internalizing problems, externalizing problems, and core syndromes such as attention problems, withdrawal, anxiety/depression, delinquent behaviors, and aggression.

Table 3. Psychosocial function
  1. aSY: surface-years; bSE: standard error; cBASC-SR: Behavior Assessment for Children Self Report; dCBCL: Child Behavior Checklist parent report; eThe BASC-SR scores reported in the table above reflect the scores of children aged 6-10 years. However, the BASC-SR was developed for children ≥ 8 years. Change in BASC-SR was, therefore, assessed among children aged ≥ 8 years as a subgroup. The results were similar to those for children aged 6-10 years except in the amalgam arm, where there was an association with interpersonal relations in children aged ≥ 8 years (P value = 0.03).

 Composite (permanent/posterior occlusal SYa)Amalgam (permanent/posterior occlusal SYa)Composite versus amalgam
  10-SY (SEb) P value 10-SY (SEb) P value P value
BASC-SRc T-Score, adjusted mean     
Emotional symptoms index1.7 (0.5)0.002-0.5 (0.7)0.49Not reported
Clinical maladjustment1.4 (0.6)0.02-0.4 (0.8)0.58Not reported
School maladjustment0.5 (0.7)0.420.5 (0.8)0.56Not reported
Personal adjustment-2.2 (0.5)< 0.00010.7 (0.7)0.35Not reported
Anxiety1.3 (0.6)0.03-1.2 (0.8)0.13Not reported
Depression1.0 (0.5)0.050.5 (0.7)0.49Not reported
Attitude to school0.8 (0.7)0.240.4 (0.9)0.67Not reported
Interpersonal relations-1.5 (0.5)0.0010.7 (0.6)0.25eNot reported
CBCLd Change Score, adjusted mean     
Competence-0.5 (0.7)0.47-0.3 (0.9)0.74Not reported
Total problem behaviors0.1 (0.7)0.93-1.4 (1.0)0.15Not reported
Internalizing problems0.7 (0.8)0.37-1.6 (1.0)0.11Not reported
Externalizing problems-0.4 (0.7)0.53-0.9 (0.9)0.34Not reported
Attention problems-0.1 (0.4)0.75-0.6 (0.5)0.27Not reported
Withdrawn0.6 (0.4)0.15-0.5 (0.5)0.33Not reported
Anxious/depressed0.8 (0.4)0.07-1.1 (0.5)0.03Not reported
Delinquent behaviors0.7 (0.5)0.16-1.4 (0.6)0.02Not reported
Aggression0.02 (0.4)0.95-0.05 (0.5)0.3Not reported
Table 4. Physical development
  1. BMI: body mass index; SE: standard error.

 CompositeAmalgamComposite versus amalgam
  5-year change (SE) 5-year change (SE) β (SE) P value
Growth outcome in girls    
Body fat percentage8.8 (0.7)7.7 (0.8)0.05 (0.83)0.95
BMI-for-age z-score0.36 (0.06)0.21 (0.07)0.08 (0.12)0.49
Height30.7 (0.5)31.2 (0.5)0.77 (1.18)0.51
Growth outcome in boys    
Body fat percentage4.9 (0.9)5.7 (0.9)0.57 (0.82)0.49
BMI-for-age z-score0.13 (0.08)0.25 (0.07)-0.21 (0.23)0.36
Height34.4 (0.6)33.5 (0.6)0.48 (0.83)0.56

The authors concluded that greater exposure to composite restorations was associated with impaired psychosocial function in children whereas no adverse psychosocial outcomes were observed with greater amalgam treatment levels. No between-group comparison was reported.

The growth outcomes considered were body fat percentage, body mass index (BMI) and height. There were no statistically significant differences in physical development in children given composite and amalgam restorations.

Discussion

Summary of main results

We meta-analyzed seven trials reporting outcome data on failure rate, secondary caries, fracture of restoration, and adverse effects. However, due to the poor reporting and analysis of the data from the split-mouth studies, only evidence from the two parallel group trials are presented in Summary of findings for the main comparison to inform this review. The results of the two parallel group trials suggest that composite restorations are almost twice at risk of failing, and for having secondary caries compared with amalgam restorations. There was no evidence of a difference in fracture rates between amalgam and composite restorations. Though the evidence from the two trials may be considered insufficient, they are supported by five additional split-mouth trials, which found similar results on all three outcomes. While the results of the two parallel group trials showed greater effect size, they were less precise than the pooled estimate of all seven trials. As none of the adverse effects were reported in more than one study, the results should be interpreted with caution.

Overall completeness and applicability of evidence

The included studies were randomized controlled trials (RCTs) that compared resin composite restorations with amalgam restorations in permanent posterior teeth. Follow-up period ranged between three and seven years. We reported outcome results on failure rate, secondary caries, fracture of restorations, and adverse effects in this review. The event of a failure is reported rather than the non-event of survival. There was a limited number of studies reporting on adverse effects associated with either amalgam or compostie restorations, and the generalisability of the findings from these trials to populations other than healthy children (e.g children or adults with potential mercury-sensitive health conditions such as chronic kidney disease) is unclear. In addition, there is recent emerging research looking into genetic susceptibility to the adverse neurological effects of mercury exposure in children with effects manifested predominantly among boys. It is acknowledged that in order to complete a comprehensive systematic review of adverse events, observational studies would need to be included.This was not the focus of this review; only adverse events identified in the included trials have been reported.

We found insufficient outcome data on the cost of restorations, therefore, this outcome was not covered in the review.

The dental material industry is continuously evolving and improving the products that clinicians use. Most of the included studies were conducted in the 1990s. Some of the materials used in the studies included for the review may no longer be in use or may have been replaced by products with better mechanical properties and better resistance to wear, shrinkage, and fracture. In that case, the results of this review may not be a true reflection of the quality of new restorations that are currently in use.

Quality of the evidence

The body of evidence is based on the results of two parallel group RCTs (involving 1006 participants and 3010 restorations) supported by an additional five split-mouth RCTs. Evidence on failure rate and secondary caries were assessed as low quality due to high risk of bias and inconsistency while evidence on fracture of restoration was of moderate quality. High risk of bias was due to lack of blinding and allocation concealment. Differences in oral hygiene may have contributed to the inconsistency observed with the failure rate and secondary caries outcomes owing to age differences of participants in both trials (mean age 7.9 and 10.2 years). Inconsistency may have also resulted from the difference in adhesives used for composite restoration in the studies. The trial that found an association between composite restoration and impaired psychosocial function had reported that participants received additional composite restoration in cases where any anterior teeth needed restoration. This may have amplified the effects of composite restoration on psychosocial function.

Potential biases in the review process

There were units of analysis issues with all the studies as even the parallel group studies had more than one filling per person, and the data were analyzed without taking into account the clustering. This will mean that the confidence intervals for the effect estimates were smaller than they should be, but this effect will be very small. The effect for the split-mouth studies is unknown as there is lack of clarity in their reporting and this is why they have not been included in the primary analysis.

Agreements and disagreements with other studies or reviews

The results obtained in the process of the present systematic review are consistent with the conclusions of the systematic review performed by the Canadian Agency of Drugs and Technologies in Health (CADTH 2012), which presented safety, efficacy, and cost results. However, in the two studies in CADTH 2012 presenting efficacy data, the duration of follow-up was inadequate for inclusion in this review.

Authors' conclusions

Implications for practice

There is low-quality evidence to suggest that resin composites lead to higher failure rates and risk of secondary caries than amalgam restorations. This review reinforces the benefit of amalgam restorations and the results are particularly useful in parts of the world where amalgam is still the material of choice to restore posterior teeth with proximal caries. The review found insufficient evidence to support or refute any adverse effects amalgam or composite restorations may have on patients. However, emerging research is highlighting issues around genetic susceptibility to mercury. The decision for a global phase-down of amalgam (Minamata Convention on Mercury) will restrict the future use of amalgam.

Implications for research

This review indicates that there are higher failure rates with resin composite than amalgam restorations. The included studies date back to 2007 and composite dental restorative materials have advanced considerably since then. Since the proposed discontinuation of use of amalgam depends on quality improvement of non-mercury-based alternative restorative materials (BDA 2013), there is need for continued focus on new research demonstrating the long-term effectiveness of the latest improved composite materials, techniques, and instruments for placing them. If future studies use a split-mouth design then it is imperative that the data are analyzed and reported appropriately taking the clustering of sites within participants into account (Lesaffre 2009).

Acknowledgements

We want to thank the following people.

Krishna Aravamudhan and Julie Frantsve-Hawley (American Dental Association) and Aronita Rosenblatt (University of Pernambuco, Brazil) for their help in finding some articles.

Luisa Fernandez Mauleffinch (Cochrane Oral Health Group) for her help in amending the protocol.

Anne Littlewood (Cochrane Oral Health Group) for her contribution in bibliographic searching.

Helen Worthington, Tanya Walsh (Cochrane Oral Health Group), and Marta Roqué-Figuls (Iberoamerican Cochrane Center) for their contribution in the methodological issues.

Agustin Ciapponi (IECS Cochrane Center Co-ordinator, Iberoamerican Cochrane Network, Argentina) for his constant support.

Huan Lu for her help in completing the protocol.

Data and analyses

Download statistical data

Comparison 1. Primary and secondary outcomes
Outcome or subgroup titleNo. of studiesNo. of participantsStatistical methodEffect size
1 Failure rate75200Risk Ratio (M-H, Fixed, 95% CI)1.78 [1.47, 2.17]
1.1 Failure rate - parallel group studies23010Risk Ratio (M-H, Fixed, 95% CI)1.89 [1.52, 2.35]
1.2 Failure rate - split-mouth studies52190Risk Ratio (M-H, Fixed, 95% CI)1.42 [0.90, 2.24]
2 Secondary caries64036Risk Ratio (M-H, Fixed, 95% CI)2.11 [1.66, 2.69]
2.1 Secondary caries - parallel group studies23010Risk Ratio (M-H, Fixed, 95% CI)2.14 [1.67, 2.74]
2.2 Secondary caries - split-mouth studies41026Risk Ratio (M-H, Fixed, 95% CI)1.50 [0.43, 5.21]
3 Fracture of restorations23010Risk Ratio (M-H, Fixed, 95% CI)0.87 [0.46, 1.64]
Analysis 1.1.

Comparison 1 Primary and secondary outcomes, Outcome 1 Failure rate.

Analysis 1.2.

Comparison 1 Primary and secondary outcomes, Outcome 2 Secondary caries.

Analysis 1.3.

Comparison 1 Primary and secondary outcomes, Outcome 3 Fracture of restorations.

Appendices

Appendix 1. Cochrane Oral Health Group's Trials Register search strategy

From October 2013, searches of the Cochrane Oral Health Group's Trials Register were conducted using the Cochrane Register of Studies and the search strategy below:

#1 ((tooth or teeth or molar* or bicuspid* or "Class I" or "Class II"):ti,ab) AND (INREGISTER)
#2 ((fill* or restor*):ti,ab) AND (INREGISTER)
#3 (#1 and #2) AND (INREGISTER)
#4 (amalgam*:ti,ab) AND (INREGISTER)
#5 ((resin* and composite*):ti,ab) AND (INREGISTER)
#6 (("bisphenol A-Glycidyl methacrylate" or compomer* or Bis-GMA):ti,ab) AND (INREGISTER)
#7 (("enamel bond*" or (concise and resin*) or (white and sealant*) or "conclude resin*" or Adaptic or Delton or Epoxylite-9075 or (Kerr and seal*) or Nuva-seal or Panavia or Retroplast or Silux):ti,ab) AND (INREGISTER)
#8 (#5 or #6 or #7) AND (INREGISTER)
#9 (#3 and #4 and #8) AND (INREGISTER)

In May 2012, a search of the Cochrane Oral Health Group's Trials Register was conducted using the Procite software and the search strategy below:

(((tooth or teeth or molar* or bicuspid* or "Class I" or "Class II") and (fill* or restor*)) and (amalgam and ((resin* and composite*) or "bisphenol A-Glycidyl methacrylate" or compomer* or Bis-GMA or "enamel bond*" or (concise and resin*) or (white and sealant*) or "conclude resin*" or Adaptic or Delton or Expoylite-9075 or (Kerr and seal*) or Nuva-seal or Panavia or Retroplast or Silux)))

Appendix 2. CENTRAL search strategy

#1 MeSH descriptor Dental Restoration, Permanent explode all trees
#2 MeSH descriptor Dental Restoration, Temporary explode all trees  
#3 ( (tooth in All Text or teeth in All Text or molar* in All Text or bicuspid* in All Text or "Class I" in All Text or "Class II" in All Text) and (restor* in All Text or fill* in All Text) )
#4 (#1 or #2 or #3)
#5 MeSH descriptor Dental amalgam this term only
#6 amalgam* in Title, Abstract or Keywords
#7 (#5 or #6)
#8 MeSH descriptor Composite resins explode all trees
#9 ( (resin* in Title, Abstract or Keywords near/3 composite* in Title, Abstract or Keywords) or "bisphenol A-Glycidyl methacrylate" in Title, Abstract or Keywords or compomer* in Title, Abstract or Keywords or Bis-GMA in Title, Abstract or Keywords)
#10 ("enamel bond*" in Title, Abstract or Keywords or (concise in Title, Abstract or Keywords near/3 resin* in Title, Abstract or Keywords) or (white in Title, Abstract or Keywords near/3 sealant* in Title, Abstract or Keywords) or "conclude resin*" in Title, Abstract or Keywords or Adaptic in Title, Abstract or Keywords or Delton in Title, Abstract or Keywords or Epoxylite-9075 in Title, Abstract or Keywords or (Kerr in Title, Abstract or Keywords near/5 seal* in Title, Abstract or Keywords) or Nuva-seal in Title, Abstract or Keywords or Panavia in Title, Abstract or Keywords or Retroplast in Title, Abstract or Keywords or Silux in Title, Abstract or Keywords)
#11 (#8 or #9 or #10)
#12 (#4 and #7 and #11)

Appendix 3. MEDLINE via OVID search strategy

1. Dental restorations, permanent/
2. Dental restorations, temporary/
3. ((tooth or teeth or molar$ or bicuspid$ or "Class I" or "Class II") and (restor$ or fill$)).ti,ab.
4. or/1-3
5. Dental amalgam/
6. amalgam$.ti,ab.
7. or/5-6
8. exp Composite resins/
9. ((resin$ adj3 composite$) or "bisphenol A-Glycidyl methacrylate" or compomer$ or Bis-GMA).ti,ab.
10. ("enamel bond$" or (concise adj3 resin$) or (white adj3 sealant$) or "conclude resin$" or Adaptic or Delton or Epoxylite-9075 or (Kerr adj5 seal$) or Nuva-seal or Panavia or Retroplast or Silux).ti,ab.
11. or/8-10
12. 4 and 7 and 11

Appendix 4. EMBASE via OVID search strategy

1. Tooth filling/
2. ((tooth or teeth or molar$ or bicuspid$ or "Class I" or "Class II") and (restor$ or fill$)).ti,ab.
3. 1 or 2
4. Dental alloy/
5. amalgam$.ti,ab.
6. or/4-5
7. exp Resin/
8. ((resin$ adj3 composite$) or "bisphenol A-Glycidyl methacrylate" or compomer$ or Bis-GMA).ti,ab.
9. ("enamel bond$" or (concise adj3 resin$) or (white adj3 sealant$) or "conclude resin$" or Adaptic or Delton or Epoxylite-9075 or (Kerr adj5 seal$) or Nuva-seal or Panavia or Retroplast or Silux).ti,ab.
10. or/7-9
11. 3 and 6 and 10

Appendix 5. LILACS search strategy

(Mh dental restorations, permanent or Mh dental restorations, temporary or (tooth or teeth or diente$ or dente$ or molar$ or premolar$ or bicuspid$ or "Class I" or "Class II") and (restor$ or restaura$ or fill$)) [Words] and (Mh Dental amalgam or amalgam$) AND (Mh Composite resins or (resin$ and composite$) or (resin$ and compuesta$) or (resin$ and composta$) or "bisphenol A-Glycidyl methacrylate" or compomer$ or Bis-GMA or "enamel bond$" or (concise$ and resin$) or (white and sealant$) or "conclude resin$" or Adaptic or Delton or Epoxylite-9075 or (Kerr and seal$) or Nuva-seal or Panavia or Retroplat or Silux or Compómeros or Compômeros) [Words]

What's new

DateEventDescription
21 May 2014AmendedConclusions edited to reflect received feedback.

Contributions of authors

Conceiving the review: María Graciela Rasines Alcaraz (GR), Patrick Roger Schmidlin (PRS).
Co-ordinating the review: GR.
Developing search strategy: Dell Davis (DD).
Handsearching of relevant journals: GR.
Retrieve from literature's references list: GR.
Contacting authors: GR.
Obtaining and screening data on unpublished studies: Analia Veitz-Keenan (AVK), Philipp Sahrmann (PS), PRS, GR.
Screening search results: AVK, GR.
Screening retrieved papers against inclusion criteria: PS, PRS.
Appraising quality of papers: AVK, PS, PRS, GR.
Extracting data from papers: AVK, PS, PRS, GR.
Entering data into RevMan: GR.
Analyses of data: GR.
Interpretation of data: AVK, PS, PRS, GR.
Writing the review: AVK, PS, PRS, GR.
Revised the review: Zipporah Iheozor-Ejiofor (ZIE).

Declarations of interest

M Graciela Rasines Alcaraz, Analia Veitz-Keenan, Philipp Sahrmann, Patrick Roger Schmidlin, Dell Davis, Zipporah Iheozor-Ejiofor: no interests to declare.

Sources of support

Internal sources

  • No sources of support supplied

External sources

  • Cochrane Oral Health Group Global Alliance, UK.

    All reviews in the Cochrane Oral Health Group are supported by Global Alliance member organisations (British Association of Oral Surgeons, UK; British Association for the Study of Community Dentistry, UK; British Orthodontic Society, UK; British Society of Paediatric Dentistry, UK; British Society of Periodontology, UK; Canadian Dental Hygienists Association, Canada; Mayo Clinic, USA; National Center for Dental Hygiene Research & Practice, USA; New York University College of Dentistry, USA; and Royal College of Surgeons of Edinburgh, UK) providing funding for the editorial process (http://ohg.cochrane.org/).

  • National Institute for Health Research (NIHR), UK.

    CRG funding acknowledgement:
    The NIHR is the largest single funder of the Cochrane Oral Health Group.

    Disclaimer:
    The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health.

Differences between protocol and review

The participant inclusion criterion in the protocol was originally restricted to adults and adolescents. Tooth type (permanent posterior teeth) was considered more important as a criterion than age group, therefore, studies on children were included. Only data on permanent posterior teeth were reported in this review.

Participant satisfaction could not be analyzed as none of the randomized controlled trials had data about this variable.

Cost-effectiveness could not be calculated because of partial reporting.

In the protocol, survival rate was listed as the primary outcome but the review lists failure rate as primary outcome. Failure rate is reported in this review as a proxy for survival rate.

We aimed to minimize potential reporting biases including publication bias, time lag bias, multiple (duplicate) publication bias, and language bias by constructing a funnel plot. However, we were unable to achieve this since we had fewer than 10 studies.

Only dichotomous data were available.

The review used random-effects models unless there were fewer than four studies, when fixed-effect models were used, as this is general policy for the Cochrane Oral Health Group. The protocol stated random-effects models only.

Characteristics of studies

Characteristics of included studies [ordered by study ID]

Casa Pia 2007

Methods

Study design: parallel group RCT

Conducted in: Lisbon, Portugal

Number of centers: 1 at Lisbon Faculty of Dental Medicine

Recruitment period: started in 1996

Funding source: National Institute of Dental & Craniofacial Research

Participants

Inclusion criteria: children born from 1986 through 1989. At least 1 carious lesion in a permanent posterior tooth. Urinary mercury concentration less than 10 μg/L. Blood lead concentration of less than 15 μg/dL. An IQ score at least 67 on Comprehensive Test of Nonverbal Intelligence

Exclusion criteria: prior exposure to dental amalgam, interference health condition

Age: 8-12 years

Caries risk status: unclear

Location of teeth filled: 1545 permanent molars and 203 premolars

Type of cavity filled: 879 Class I restorations and 869 Class II restorations

Number randomized: 507 children

Number evaluated: 472

Interventions

Comparison: composite versus amalgam

Group A: 233 children received 892 composite restorations

Group B: 239 children received 856 amalgam restorations

Type of moisture control: the restorations were placed using rubber dam isolation whenever possible

Duration of follow-up: 7 years

Outcomes
  1. Failure rate, estimated at 7 years

  2. Secondary caries, estimated at 7 years

  3. Fracture of restoration, estimated at 7 years

  4. Adverse sentinel health events

  5. Neurobehavioral assessment of memory, attention concentration, and motor/visuomotor domains, as well as nerve conduction velocities, estimated at year 1, 2, 3, 4, 5, 6, and 7

Notes

Sample size calculation: selected to ensure adequate power for detecting 2 potential scenarios

The first scenario was a small but near-uniform effect of 0.3 SD for the 3 neurobehavioral outcomes, and half of that (0.15 SD) for the nerve conduction outcome. The effect size of 0.3 SD represents a shift that would cause the proportion of abnormally low values in a normally distributed population to increase from 2.5% to 5.0%, thus doubling the proportion classified as abnormally low
For the second scenario, a potential effect in only 1 of the 4 outcomes was of interest, so an effect size of 0.5 SD in the nerve conduction outcome was used, with no effects in the others
A sample size of 400 (200 in each group) through 5 years of follow-up provided adequate power (97%) to detect both scenarios

Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskEven though the children were randomly assigned to 1 of the 2 treatment groups, the authors did not explain which method of randomization was used
Allocation concealment (selection bias)High risk Not reported
Blinding of participants and personnel (performance bias)
All outcomes
High riskNot reported. Due to the clinical characteristics of the interventions, blinding was not possible
Blinding of outcome assessment (detection bias)
All outcomes
High riskThe restorative procedures were standardized and the dentists were calibrated before starting the trial but there is no indication that assessors were blinded or different from the operators
Incomplete outcome data (attrition bias)
All outcomes
Low riskNo children were missed and all of them were analyzed in the group that they were allocated by randomization
Selective reporting (reporting bias)Low riskOf the initial 507 children, 19 had no dental exam after baseline and 16 had no restoration to posterior teeth at baseline. 472 children (93%) were followed up for 1 years
Other biasLow riskNo other bias apparent

Cunningham 1990

Methods

Study design: RCT of split-mouth design

Conducted in: Liverpool, UK.

Number of centers: 3 dentists, 1 based at Liverpool Dental Hospital, the others being general practitioners

Recruitment period: not reported

Funding source: unclear

Participants

Inclusion criteria: teeth requiring the treatment of Class I and Class II carious lesions

Exclusion criteria: unclear

Age: not reported

Caries risk status: unclear

Location of teeth filled: not reported

Type of cavity filled: O: 83 cavities, MO: 140 cavities, DO: 164 cavities, MOD: 122 cavities

Number randomized: 605 cavities (Class I or Class II lesions) were randomly assigned to be restored with 2 different amalgams and 3 different composites

Number evaluated: 509 restorations were reviewed

Interventions

Comparison: composite versus amalgam

Group A: 309 composite restorations

Group B: 200 amalgam restorations

Type of moisture control: unclear

Duration of follow-up: 3 years

Outcomes
  1. Failures and fractures of the restorations, estimated at year 3

  2. Contact points, estimated at 6, 12, 24, and 36 months

  3. Gingival inflammation, estimated at 6, 12, 24, and 36 months

  4. Marginal stain and caries, estimated at year 3

  5. Color match, estimated at year 3

NotesSample size calculation: unclear
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskEven though the teeth were randomly assigned to treatment groups; the authors did not explain which method of randomization was used to generate the allocation sequence
Allocation concealment (selection bias)Low riskThere was no information about the method used to conceal the allocation sequence; however, due to the study design (split-mouth), a lack of allocation concealment was unlikely to introduce bias
Blinding of participants and personnel (performance bias)
All outcomes
High riskNot reported. Due to the clinical characteristics of the interventions, blinding was not possible
Blinding of outcome assessment (detection bias)
All outcomes
High riskDue to the clinical characteristics of the interventions, blinding was not possible
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskOf the original 605 restorations, 509 could be examined at 3 years and the losses were said to have been evenly distributed across the trial arms but no data showing this. Follow-up 84.1%
Selective reporting (reporting bias)Low riskAll the data were well reported
Other biasHigh riskUnit of analysis error - the total number of participants was not indicated in the paper. There were 5 materials in consideration and each tooth was randomized to 1 of them but it is not really clear which is the real number of restoration per participants

Hendriks 1986

Methods

Study design: RCT of split-mouth design

Conducted in: unclear

Number of centers: 3 operators

Recruitment period: unclear

Funding source: unclear

Participants

Inclusion criteria: not reported

Exclusion criteria: not reported

Age: adults

Caries risk status: unclear

Location of teeth filled: 108 permanent molars and 124 premolars

Type of cavity filled: not reported

Number randomized: 242 cavities

Number evaluated: 232 cavities

Interventions

Comparison: composite versus amalgam

Group A: 174 composite restorations

Group B: 58 amalgam restorations

Type of moisture control: rubber dam

Duration of follow-up: 3 years

OutcomesFailures of restorations estimated at year 3
NotesSample size calculation: not reported
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskThe 4 materials within each series were distributed at random over the teeth selected for restoration and the participants were assigned at random to 1 of 3 operators. The authors did not explain which method of randomization was used
Allocation concealment (selection bias)Low riskThere was no clarification in the paper about allocation concealment; however, due to the design of the study (split-mouth), a lack of allocation concealment was unlikely to introduce bias
Blinding of participants and personnel (performance bias)
All outcomes
High riskNot reported. Due to the clinical characteristics of the interventions, blinding was not possible
Blinding of outcome assessment (detection bias)
All outcomes
High riskDue to the clinical characteristics of the interventions, blinding was not possible
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskThe 3-year retrieval percentage of both the participants and restoration was 96%. However, the dropout rate was not reported by trial arm
Selective reporting (reporting bias)Low riskAll the data were well reported
Other biasLow riskNo other bias apparent

Letzel 1989

Methods

Study design: multicenter RCT, split-mouth design

Conducted in: Liverpool (UK), London (UK), Manchester (UK), North Carolina (USA), Indianapolis (USA), South Illinois (USA), Philadelphia (USA), Gotenburg (Sweden), Nijmegen (Netherlands), Leuven (Belgium), Louvain (Belgium), Bonn (Germany)

Number of centers: 12

Recruitment period: not reported

Funding source: ICI Dental Imperial Chemical Industries, Macclesfield, UK

Participants

Inclusion criteria: adults with teeth requiring posterior Class I or II restorations. Sound tooth or a sound restored tooth in proximal contact with each of the teeth were included

Exclusion criteria: people who might have been unable to return for 5 years or who required special management, extensive restorative care, or cuspal replacement. Teeth requiring Class II restorations that had no proximal contact. Pairs of opposing teeth

Age: adults, age not reported

Caries risk status: unclear

Location of teeth filled: posterior teeth

Type of cavity filled: Class I and II restorations

Number randomized: 447 adults, 1164 cavities

Number evaluated: 338 adults, 693 cavities

Interventions

Comparison: composite versus amalgam

Group A: 461 composite restorations

Group B: 232 amalgam restorations

Type of moisture control: unclear

Duration of follow-up: 5 years

Outcomes

Primary outcome: failure

In order to trace the causes of failure in each case, the reasons for failure were classified according to a system described by Letzel et al in 1988. This system was designed for an evaluation of the influence of experimental variables and operators on the survival rate of restorations included in controlled clinical trials of dental amalgams
The system distinguishes 3 types of restoration failure:

Type 1 - failures directly related to the restoration (i.e. the material and the way it is manipulated into a restoration)
Type 2 - failures related to the restorative process (i.e. the result of the decision-making process of the operator)

Type 3 - failures caused by external factors

Notes

Sample size calculation: not reported

12 centers were involved in the trial but the data of only 10 centers were used in this study because they complied with the condition of fully reviewing the restorations after at least 4 years

Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Unclear riskThe authors declared that randomization was done in 5 of the centers, but there is no explanation about if the sequence generation had been at random in the other centers
Allocation concealment (selection bias)Low riskThere is no clarification in the paper about allocation concealment; however, due to the design of the study (split-mouth), a lack of allocation concealment was unlikely to introduce bias
Blinding of participants and personnel (performance bias)
All outcomes
High riskNot reported. Due to the clinical characteristics of the interventions, blinding was not possible
Blinding of outcome assessment (detection bias)
All outcomes
High riskDue to the clinical characteristics of the interventions, blinding was not possible
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskThe follow-up at 4 years was 76% for composite restorations. Dropout rate for amalgam was not clearly reported 
Selective reporting (reporting bias)High riskAll the data seemed to be well reported for composite but partially reported for amalgam, especially follow-up data
Other biasHigh riskThere were variations in practice and dropout rate among the centers and the reason for these variations was not clearly explained. Unit of analysis error - number of restorations reported but not the number of participants per restoration

NECAT 2007

Methods

Study design: parallel group RCT

Conducted in: USA

Number of centers: 5 community centers from Boston and Maine, USA

Recruitment period: 1997-2005

Funding source: unclear

Participants

Inclusion criteria: children fluent in English.

Had 2 or more posterior teeth with dental caries. Primary and permanent teeth

Exclusion criteria: had known prior or existing amalgam restorations. Had a physician diagnosed psychological behavioral, neurologic, immunosuppressive, or renal disorder

Age: 6-10 years

Caries risk status: not reported

Location of teeth filled: posterior teeth

Type of cavity filled: Class I and Class II restorations

Number randomized: 534 children

Number evaluated: 449 children

Interventions

Comparison: composite versus amalgam

Group A: 753 composite restorations

Group B: 509 amalgam restorations

Type of moisture control/tooth isolation: rubber dam

Duration of follow-up: 5 years. Evaluation every 6 months

OutcomesRate of replacement and repair of the restorations, psychosocial function (5-year follow-up), physical development (5-year follow-up)
NotesSample size calculation: not reported. We use only data from permanent teeth
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskRandomization was stratified by geographic location (Boston/Cambridge versus Farmington) and number of teeth with caries (2-4 versus 5 or more), using randomly permuted blocks within each of the 4 strata
Allocation concealment (selection bias)High riskNot reported
Blinding of participants and personnel (performance bias)
All outcomes
High riskParticipants and dentists could not be blinded to treatment assignment
Blinding of outcome assessment (detection bias)
All outcomes
High riskDue to the clinical characteristics of the interventions, blinding was not possible
Incomplete outcome data (attrition bias)
All outcomes
Low riskThe follow-up at 3 years was 84% and the losses were similar in both groups 
Selective reporting (reporting bias)Low riskAll data were well reported
Other biasLow riskNo other apparent biases

Norman 1990

Methods

Study design: RCT with split-mouth design

Conducted in: unclear

Number of centers: 1

Recruitment period: not reported

Funding source: ICI, Imperial Chemical Industries, Macclesfield, UK

Participants

Inclusion criteria: participants in need of posterior Class I and II restorations. Maximum of 4 restorations were allowed. Selection of the teeth required that there be a sound tooth or a sound restored tooth in proximal contact to the restoration. At least a portion of the restoration was required to be in contact with an opposite tooth or restoration

Exclusion criteria: not reported

Age: 28-40 years

Caries risk status: not reported

Location of teeth filled: molars and premolars

Type of cavity filled: Class I and II restorations

Number randomized: 62 participants, 160 restorations

Number evaluated: 123 restorations

Interventions

Comparison: composite versus amalgam

Group A: 80 Occlusin composite. Light cured, highly filled hybrid posterior composite resin

Group B: 43 Dispersaloy amalgam

Type of moisture control: rubber dam was used to isolate the teeth

Duration of follow-up: 5 years

Outcomes

Primary outcomes were failure and recurrent caries

Wear, marginal adaptation, anatomic form, interproximal contacts

NotesSample size calculation: not reported
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskAll restorations were placed by following a random selection chart for composite resins and amalgam
Allocation concealment (selection bias)Low riskThere was no information about the method used to conceal the allocation sequence; however, due to the design of the study (split-mouth), a lack of allocation concealment was unlikely to introduce bias
Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNot reported. Due to the clinical characteristics of the interventions, blinding was not possible
Blinding of outcome assessment (detection bias)
All outcomes
High riskDue to the clinical characteristics of the interventions, blinding was not possible
Incomplete outcome data (attrition bias)
All outcomes
Unclear risk

The follow-up at 5 years was 80.6%. However, the dropout rate was not reported by trial arm

 

Selective reporting (reporting bias)Low riskAll data were well reported
Other biasHigh riskUnit of analysis error - number of restorations reported but not the number of participants

Robinson 1988

  1. a

    D: distal; IQ: intelligence quotient; M: mesial; MOD: mesial, occlusal, and distal; O: occlusal; RCT: randomized controlled trial; SD: standard deviation.

Methods

Study design: RCT of Split-mouth design

Conducted in: Guy's Hospital, London, UK

Number of centers: 1

Recruitment period: not clear

Funding source: ICI Dental, Macclesfield, UK

Participants

Inclusion criteria: adults who required occlusal and proximo-occlusal restorations in vital premolars and molars

Exclusion criteria: mental and physical disabilities likely to prevent continued co-operation, people who would not be available for the long-term follow-up visits over the 5 years and restorations requiring cuspal replacement

Age: 19-66 years

Caries risk status: not reported

Location of teeth filled: molars and premolars

Type of cavity filled: Class I and II restorations

Number randomized: 58 participants, 98 composites and 27 amalgams

Number evaluated: 90 restorations

Interventions

Comparison: composite versus amalgam

Group A: 70 Occlusin composite

Group B: 20 Aristaloy amalgam

Type of moisture control/tooth isolation used: rubber dam isolation in 82.4% of cases

Duration of follow-up: 3 years

OutcomesFailure rate in terms of the following criteria: gingival condition, interproximal contacts, color match, anatomic form, surface roughness
NotesSample size calculation: not reported
Risk of bias
BiasAuthors' judgementSupport for judgement
Random sequence generation (selection bias)Low riskThe participants were allocated to receive composite or amalgam restoration in the ratio 3:1 from a randomized table
Allocation concealment (selection bias)Low riskThere was no information about the method used to conceal the allocation sequence; however, due to the design of the study (split-mouth), a lack of allocation concealment was unlikely to introduce bias
Blinding of participants and personnel (performance bias)
All outcomes
Unclear riskNot reported. Due to the clinical characteristics of the interventions, blinding was not possible
Blinding of outcome assessment (detection bias)
All outcomes
High riskDue to the clinical characteristics of the interventions, blinding was not possible
Incomplete outcome data (attrition bias)
All outcomes
Unclear riskThe follow-up at 36 month was 78.4% but it was not clear whether drop-out was balanced between the trial arms 
Selective reporting (reporting bias)Low riskAll data were well reported
Other biasHigh riskUnit of analysis error - number of restorations reported but not the number of participants

Characteristics of excluded studies [ordered by study ID]

StudyReason for exclusion
  1. a

    RCT: randomized controlled trial.

Allan 1977Non-RCT. Retrospective analysis of dental records
Bellinger 2006This study reports data of the New England Children's Amalgam Trial. As the data of permanent and temporary dentition were not informed separately, it was not possible to extract the data of permanent posterior teeth
Borgmeijer 1991Insufficient follow-up and incomplete data
Bryant 1994Not an RCT. No randomization
Busato 1996Not an RCT. No randomization
Cloyd 1997Not an RCT. No randomization
Collins 1998Not an RCT. No randomization
Dilley 1990It did not evaluate longevity correctly
Eames 1974Not an RCT. No randomization
Fukushima 1988Not an RCT. No randomization
Hendriks 1985Not an RCT. No randomization
Johnson 1992Not an RCT. No randomization
Knibbs 1992Not an RCT. No randomization
Kopperud 2012Not a randomized trial
Koray n.d.Unpublished. The author did not respond to the request for data
Kreulen 1993aNo long-term follow-up. No caries and fracture reporting
Kreulen 1993bThe intervention did not correspond with aims of the review
Lambrechts 1984Follow-up 18 months
Leinfelder 1975Follow-up 24 months
Leinfelder 1980As the study considered anterior and posterior restorations, it is difficult to be sure that the failures occurred in Class 1 and 2 restorations
Mair 1995No data could be extracted
Mair 1998No data could be extracted
Mannocci 2005The intervention did not correspond with aims of the review
Mjör 1993aNot an RCT. No randomization
Mjör 1993bNot an RCT
Nell 1994The intervention did not correspond with aims of the review
Pieper 1991Not an RCT. Retrospective study
Powers 1974Not an RCT. No randomization
Prati 1988Not an RCT. No randomization
Roulet 1977Follow-up 12 months
Roulet 1978Same data as Roulet 1977
Rowe 1989Not an RCT. No randomization
Rytömaa 1984Not an RCT. No randomization
Samaha 1982Not an RCT. No randomization
Shenker 2008This study report data of the New England Children's Amalgam Trial. As the data of permanent and temporary dentition were not informed separately, it was not possible to extract the data of permanent posterior teeth
Smales 1991Not an RCT. No randomization
Smales 1992The intervention did not correspond with aims of the review
Solano 1984These study data were unpublished (Master's dissertation) and could not be found for critical appraisal
Tobi 1999Randomized at tooth level but only partially analyzed and reported
Van Nieuwenhuysen 2003Not an RCT. No randomization
Walls 1988Follow-up 24 month
Welbury 1990Randomization was broken by ignoring it in 20/150 pairs of teeth
Wilson 1996It did not compare amalgam versus composite

Ancillary